[PATCH] IR: Make MDNode::dump() useful by adding addresses

[Frédéric Riss]

> On Dec 12, 2014, at 2:37 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> 
> It's horrible to inspect `MDNode`s in a debugger.  All of their operands
> that are `MDNode`s get dumped as `<badref>`, since we can't assign
> metadata slots in the context of a `Metadata::dump()`.  (Why not?  Why
> not assign numbers lazily?  Because then each time you called `dump()`,
> a given `MDNode` could have a different lazily assigned number.)
> 
> Fortunately, the C memory model gives us perfectly good identifiers for
> `MDNode`.  Add pointer addresses to the dumps, transforming this:
> 
>    (lldb) e N->dump()
>    metadata !{i32 662302, i32 26, metadata <badref>, null}
> 
>    (lldb) e ((MDNode*)N->getOperand(2))->dump()
>    metadata !{i32 4, metadata !"foo"}
> 
> into:
> 
>    (lldb) e N->dump()
>    metadata !{i32 662302, i32 26, metadata <badref:0x100706ee0>, null}
> 
>    (lldb) e ((MDNode*)0x100706ee0)->dump()
>    metadata !{i32 4, metadata !"foo”}

If it were only for debugger consumption, I’d make it totally copy-pastable:

<badref:((MDNode*)0x100706ee0)>

Not sure this is acceptable in textual IR though.

FRed

> and this:
> 
>    (lldb) e N->dump()
>    metadata !{metadata <badref>, metadata <badref>, metadata <badref>, metadata <badref>, metadata <badref>}
> 
>    (lldb) e N->getOperand(0)
>    (const llvm::MDOperand) $0 = {
>      MD = 0x00000001012004e0
>    }
>    (lldb) e N->getOperand(1)
>    (const llvm::MDOperand) $1 = {
>      MD = 0x00000001012004e0
>    }
>    (lldb) e N->getOperand(2)
>    (const llvm::MDOperand) $2 = {
>      MD = 0x0000000101200058
>    }
>    (lldb) e N->getOperand(3)
>    (const llvm::MDOperand) $3 = {
>      MD = 0x00000001012004e0
>    }
>    (lldb) e N->getOperand(4)
>    (const llvm::MDOperand) $4 = {
>      MD = 0x0000000101200058
>    }
>    (lldb) e ((MDNode*)0x00000001012004e0)->dump()
>    metadata !{}
> 
>    (lldb) e ((MDNode*)0x0000000101200058)->dump()
>    metadata !{null}
> 
> into:
> 
>    (lldb) e N->dump()
>    metadata !{metadata <badref:0x1012004e0>, metadata <badref:0x1012004e0>, metadata <badref:0x101200058>, metadata <badref:0x1012004e0>, metadata <badref:0x101200058>}
> 
>    (lldb) e ((MDNode*)0x1012004e0)->dump()
>    metadata !{}
> 
>    (lldb) e ((MDNode*)0x101200058)->dump()
>    metadata !{null}
> 
> I've left `badref` in the operand to keep it `FileCheck`-able, via:
> 
>    CHECK-NOT: badref
> 
> Another option would be:
> 
>    (lldb) e N->dump()
>    metadata !{metadata !0x1012004e0, metadata !0x1012004e0, metadata !0x101200058, metadata !0x1012004e0, metadata !0x101200058}
> 
> which would allow:
> 
>    CHECK-NOT: !0x
> 
> but IMO that's too subtle...
> 
> <0001-IR-Make-MDNode-dump-useful-by-adding-addresses.patch>